1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device and, more particularly, to a manufacturing method of a contact hole or an FET having an LDD structure.
2. Description of Related Art
In recent years, contact holes or the like with higher aspect ratios have been in demand mainly due to the increasing microminiaturization of semiconductor integrated circuits.
Contact holes are usually formed by etching insulating films by using resists or the like as masks. When a contact hole with a high aspect ratio is formed by dry etching, the pressure in the etching process is decreased in order to achieve a normal configuration and a higher selection ratio of the contact hole. To obtain the high selection ratio, a C-rich fluorocarbon gas is employed.
Using the C-rich forms a SiC layer on the surface of a silicon substrate in some cases. The SiC layer inhibits oxidation of silicon; therefore, it cannot be eliminated by a technique based on the standard sacrificing oxidation and HF etching. Further, the high resistance of the SiC layer inevitably results in an increased contact resistance because of the formed SiC layer. Hitherto, therefore, the SiC layer has been removed by isotropic radical etching that uses CF.sub.4, SF.sub.6 or the like.
The problem of the undesirable formation of the SiC layer has been occurring also in the forming process of transistors or an element separating process. The etching technique using CF.sub.4, SF.sub.6 or the like has been posing a problem because of its high etching speed, in which the underlayer, namely, the silicon layer, is undesirably etched in an attempt to remove only the SiC layer. There has been another problem in that, because the SiC layer is not usually formed evenly, the silicon underlayer in a thinner portion of the SiC layer is etched more deeply, resulting in a rough surface.